Synergistic Effects between Acid and Base Sites and Kinetic for Synthesis of Methylacrolein on the Cs-P/γ-Al₂O₃ Catalyst

Abstract

Methylacrolein (MAL) is traditionally synthesized from propanal and formaldehyde via the Mannich reaction instead of the aldol reaction in homogeneous catalytic systems due to the undesired self-condensation of propanal. Herein, the direct synthesis of MAL from propanal and trioxane via the aldol reaction was realized on an acid−base bifunctional Cs-P/γ-Al 2 O 3 catalyst, which exhibited good catalytic stability and could be prepared in a large scale with 54.5% yield and 100% selectivity. The influence of P elements on the structure and acid− base properties of Cs-P/γ-Al 2 O 3 and even on the selectivity of MAL, compared with Cs/γ-Al 2 O 3 , was elucidated through FT-IR, XRD, XPS, and CO 2 -and NH 3 -TPD characterizations in combination with catalytic activity evaluation. The synergistic effects between acid and base sites on MAL production were unveiled where the decomposition of trioxane into a formaldehyde unit followed by condensation between the formaldehyde monomer and propanal proceeded on the acid and base sites. Kinetics studies revealed that the trioxane decomposition into formaldehyde was zero-order-dependent on trioxane concentration and the condensation step conformed to the Langmuir−Hinshelwood mechanism, with activation barriers of 72 ± 0.2 and 65 ± 0.5 kJ/mol, respectively.

Continuous Synthesis of Methacrolein over Sulfonic Acid Resin Catalysts: Unraveling the Effect of Acid Strength and Solvent Permittivity

“…Meanwhile, MAL yields very little when polar solvents with high permittivity, such as DMF and glycol, are used. Similarly, Wang et al employed 1,4-dioxane as the solvent for MAL production from FA and PA over a Cs-P/γ-Al 2 O 3 catalyst and also obtained an outstanding MAL selectivity of up to 100% . It was also reported that water can be transported rapidly in hydrophobic solvents such as 1,4-dioxane as it forms smaller clusters than in the bulk phase under entropy and weak Van der Waals interaction forces .…”

“…Before performing mechanism-based kinetic calculations on the NKC-9 resin catalyst, external and internal diffusion were first eliminated by varying stirring speed and particle size (Figure S5). When the stirring speed exceeds 800 rpm, it does not affect the PA conversion rate, indicating that external diffusion has been eliminated. , Internal diffusion has a negligible influence on the PA conversion rate when particle size is less than 20–30 meshes (Figure S6). As a result, the kinetic study could be performed at an 800 rpm stirring speed and a particle size of 20–30 meshes.…”

“…When the stirring speed exceeds 800 rpm, it does not affect the PA conversion rate, indicating that external diffusion has been eliminated. 48,72 Internal diffusion has a negligible influence on the PA conversion rate when particle size is less than 20−30 meshes (Figure S6). As a result, the kinetic study could be performed at an 800 rpm stirring speed and a particle size of 20−30 meshes.…”

Synthesis of 1,3-Propanediol by Cross Aldol Reaction and Hydrogenation of Formaldehyde with Acetaldehyde

“…It is well recognized that both acidic and basic properties are crucial for the aldol reactions. ,,− The distribution and total number of acidic and basic sites were quantitatively determined with NH 3 - and CO 2 -TPD, respectively. The desorption temperature reflected the strengths of the acidic or basic sites, and a higher desorption temperature meant stronger acidic or basic strength .…”

Au Nanoparticle Catalysts on NiO-Decorated MgO–Al2O3 Supports for Efficient Oxidative Esterification of Methylacrolein to Methyl Methacrylate

“…As an important organic chemical raw material, methyl methacrylate (MMA) is widely used in coatings, emulsion resins, adhesives, textile sizing materials, medical functional materials, etc. , It is mainly used as a polymeric monomer to produce its polymers and copolymers and can also produce high-carbon MMA through transesterification. , At present, the main industrial process methods for MMA production are the acetone cyanoalcohol method and the isobutene method. The acetone cyanoalcohol method required highly toxic HCN, acetone, and concentrated sulfuric acid, which was dangerous and required high quality equipment (process 1).…”